Just got Turn Left (& dewing question)

[JamesK]

I just got Turn Left- even though Amazon said it would only come Wednesday- but I arn't complaining, it looks awesome. Bigger than I thought it would be too and I'm well pleased with how it lies open. Wanted to test it out as soon as possible- but cloudy skies all day, predicably. I just hope I will be able to view some of the high magnification doubles- my dept. store scope takes a massive jump from 85x to a bad quality 175x- just so they can print big numbers on the box, I think. I did read that Galileo did all his work with a 1 inch scope- the paragraph was along the lines of "So stop moaning about small mirrors and get out there."

Went out on Saturday Night though, and saw the Orion Nebula, which was slightly immense- and Saturn with rings (and i'm convinced I saw a hint of a moon- altough the info on starry night tells me this is unlikley) which was quite possibly epic. Unforunatly, as the night progressed I got a gradual deteriotion of optics- stars looked like lines rather than points and got a prisim effect glow surrounding brighter objects. I noticed condensation down the body of my 76x700 reflector I am lead to believe this is due to dewing- is this a long-term problem, or will the optics go back to normal? How can I stop this happening? Is this normal for a reflector, all I can find on the net is stuff about lenses, not mirrors! (When I googled it I didn't get much good info).

However, I'm going out Wednesday as the bbc predicts clear skies. We can but hope.

Thanks, James

[Ford Prefect]

Hi James

Dewing is a problem we all have to deal with to a greater or lesser extent. Its caused by a temperature differential between the glass in your scope and the outside air temperature.

There are a couple of ways of dealing with dewing, one very cheep way is to use a hairdryer to warm the glass in your scope. The other way is to buy a dew controller and heater strips. have a look here Dew Prevention - Astrozap Dual Channel Dew Heater Controller

You may also want to consider a dew shield if you haven't already got one.

Cheers Jon

[Helen]

As well as checking your scope for dew have a look at the eyepeice. If that's dewed up take it into the warm for a bit.

You'll have great fun with the book - lots of us cut our astronomy teeth on that book!

Helen

[JamesK]

Thanks guys- I gather from replies that this is not a long term problem?

[DemonicOmelette]

Can you use a dew shield on a reflector? I thought it was just for a refractor, to "extend" the tube past the main lens? On a reflector, the tube is already extended way past the main mirror... Or am I misunderstanding everything?

[crepitis]

Theres a post somewhere on SGL about making a homemade dew shield (maybe by astro baby ?) for a reflector, try a search for it.

[themos]

Condensation on the body (the tube) of the telescope does not affect the view. In my experience, the first thing to dew up in a reflector is the secondary mirror. A blast of warm air on it will soon get rid of the dew. A dewshield should help avoid this issue in the first place.

[beamish]

They're easy enough to make from cheap camping mats from lidl etc

[ZOG]

Can you use a dew shield on a reflector? I thought it was just for a refractor, to "extend" the tube past the main lens? On a reflector, the tube is already extended way past the main mirror... Or am I misunderstanding everything?

The bit you're misunderstanding is that it is usually the secondary that dews up, and that is at the top of the tube. As has been said, a dewshield made from a camping mat or similar can be a great help.

[beamish]

A dew-shield works wonderfully well to help minimise reflections and stray light from streetlamps